Since the first derivation of stem cells (e.g. human embryonic stem cells (hES)) (THOMSON, 1998) much attention has been drawn to the stein cell field, mainly, because of their potential role in cell therapy and regenerative medicine (MOUNTFORD, 2008), as well as their use for screening new targets in drug discovery (POUTON, 2007). However, their use in clinical therapies is limited because an environment free of animal contaminants is necessary due to the highly potential risks involving carrying non-human pathogens in humans (MARTIN, 2005). Additionally, for cultivating stem cells, an environment free of human compounds is imperative since human-preferred pathogens can be carried in this scenario.
hES have been isolated in co-culture with inactivated murine embryonic fibroblasts (MEFs) (THOMSON, 1998), where these cells are working as feeders of the process, releasing factors and matrix that supports hES growth in undifferentiated state (CHIN, 2007). The use of feeder cells provides a huge font of animal contamination but also provides the major sources of variability, since many parameters such as: background and source of mice, confluence and time after plating have been already demonstrated to affect hES culture. It is estimated that over 90% of the research involving hES use feeder co-cultures to maintain pluripotency (FERNANDES, 2010). The main problem in removing co-culturing techniques in stem cell cultures is the lack of knowledge and understanding regarding the key factors released by these cells (LIM & BODNAR, 2002; PROWSE, 2005).
Likewise, the standard media used with feeder cells includes serum-substitutes, e.g., Knockout Serum Replacement (KSR) (Invitrogen), which is replete with animal compounds, thus, making the translation to cell therapy even more difficult. Moreover, its formulation is not fully known (GARCIA-GONZALO, 2008). Once again, this media is used in over 90% of stein cell research (FERNANDES, 2010).
Alternatives to feeder conditioned and KSR based media are main concerns in the stein cell and induced pluripotent stein (iPS) cell fields. Few groups have been able to identify factors and generate new media that do not require feeder cells or even KSR in its formulation (LUDWIG, 2006; WANG, 2007). However, these studies share few things in common; all of them require a non-animal matrix, called Matrigel, as a proper surface for hES attachment. Thus, all media are mainly made of animal components, adding no benefits to the replacement of the KSR. Nevertheless, all of them lack a consistent and robust methodology of optimization, characterized by a lack of an empiric approach, leading to formulations that are not ideal, making animal components replacement for recombinant proteins unfeasible.
In that sense, it is clear that the development of an optimized, chemically defined, xeno-free and cost-effective culture medium must be generated in order to overcome one of the most important bottlenecks for future FDA-approved stem cell therapy.